Faulty cylinder 4 glow plug (open circuit, high resistance or shorted element); Corroded, loose or damaged glow plug connector or terminal on cylinder 4; Damaged wiring between the glow plug control module and cylinder 4 plug (chafing, high resistance, open or short circuit); Glow plug control module fault or failing output driver for cylinder 4; Poor earth or low battery or supply voltage affecting the glow plug circuit; Outdated or faulty control unit software where the manufacturer lists it as a known cause.

P06C8

Cylinder 4 Glow Plug Incorrect.

Generic
Powertrain
Generic code
Low severity

How this code is built

P: SystemPowertrain
0: Defined bySAE, the same on every car
6: AreaComputer and output circuits
C8: FaultThe specific fault in that area

What it means

P06C8 means the engine or glow plug control unit has judged the cylinder 4 glow plug to be operating incorrectly. The unit monitors the plug's current draw, resistance or driver feedback during heating, and it saw a value outside the expected range. The exact test and limits depend on the vehicle and glow plug system, so check the manufacturer's data for the model.

Symptoms

Glow plug or engine warning light on
Hard starting or extended cranking when cold
White smoke and rough running on cold start-up
Misfire or uneven idle on cylinder 4 until the engine warms up
Increased diesel knock on cold start-up

Possible causes

Faulty cylinder 4 glow plug (open circuit, high resistance or shorted element)likely
Corroded, loose or damaged glow plug connector or terminal on cylinder 4likely
Damaged wiring between the glow plug control module and cylinder 4 plug (chafing, high resistance, open or short circuit)possible
Glow plug control module fault or failing output driver for cylinder 4possible
Poor earth or low battery or supply voltage affecting the glow plug circuitpossible
Outdated or faulty control unit software where the manufacturer lists it as a known causerare

How to diagnose

Read all stored and pending codes and the freeze frame data, noting engine temperature, battery voltage and whether other glow plug codes are present.
Check the battery condition and charging voltage, as low voltage can upset glow plug diagnostics.
Visually inspect the cylinder 4 glow plug connector, terminal and wiring for corrosion, heat damage, chafing or looseness.
Check the glow plug control module connector, its fuses and relays, and its supply and earth connections.
Measure the cylinder 4 glow plug resistance with the plug disconnected and compare it with the manufacturer's specification, and compare it with the other plugs.
Check the wiring from the module to the plug for continuity and for shorts to earth or supply.
Use a scan tool with live data or actuator tests, where supported, to see the cylinder 4 glow plug current or status while it is energised.
Check for any software updates or technical bulletins for the model and engine before replacing the control module.

How to fix

Replace the faulty cylinder 4 glow plug, following the correct torque and removal procedure for the engine.
Clean or replace a corroded or damaged connector or terminal.
Repair or replace damaged wiring between the control module and the glow plug.
Restore a poor earth or supply connection and correct any battery or charging faults.
Replace the glow plug control module if the output is faulty and the wiring and plug test good.
Apply a manufacturer-approved software update only if an outdated calibration is a documented cause for that vehicle.

Can I keep driving?

Low severity

The car can usually be driven, but cold starting may become harder and a seized plug can be difficult to remove later. Book it in soon, especially before cold weather.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.